Need help/advice on how to fill in a groove/trench on a model's surface
Solved it to my standards. I selected a loop of vertices around and above the trench, hid it and removed the trench. Then I un-hid the loop and made some edges that ran across the new gap. Filled in the holes with faces made from the new edges and the loop. 

Not the best or most elegant solution, but I wanted to get it done ASAP. Please let me know if anyone has a better way of doing it.